Mobile Serious Games are new kind of Serious Games which are running on mobile devices, mainly on Smartphones. With continuously increased power and User Interface facilities, they constitute an alternative to the usual entertainment applications proposed on Smartphones. To design and implement such applications, a methodological assistance and development support are required. In this paper, we present our contribution to rapid prototyping for Mobile Serious Games in which we propose to augment App Inventor for Android framework with a methodological assistance. This proposition is based on a study in which we asked to 116 students to use this framework for the development of mobile applications. The results are presented (thematic domain, targeted users, components used...) and we discuss the relevance of using such a tool to achieve rapid prototyping for mobile Serious Game.